Journal of Antimicrobial Chemotherapy, Vol 40, 667-672, Copyright © 1997 by The British Society for Antimicrobial Chemotherapy
I Foley and P Gilbert
Perfused biofilms of Enterococcus faecalis reached a pseudo-steady state,
with respect to bioburden and the numbers of cells liberated within the
perfusates. Biofilm growth rate was slow (approximately 0.006 doublings/h)
relative to batch culture (approximately 0.01 doublings/h). MICs were
determined for vancomycin (0.12 mg/L) and teicoplanin (1.2 mg/L) in batch
culture. Steady-state biofilms (24 h and 48 h) were perfused continuously
for 96 h with medium containing antibiotic at 4 X MIC. Susceptibility was
assessed as cfu in the perfusate, indicating growth inhibition, and as cfu
for the parent biofilm. Vancomycin at these levels had little or no effect
on either parameter, whilst teicoplanin produced a temporary (30 h)
reduction in growth rate (99.99% for 24 h biofilms, 50% for 48 h biofilms).
Antibiotic concentrations were raised to therapeutic (trough) levels
(vancomycin, 5 mg/L; teicoplanin, 12 mg/L) and applied continuously to 24 h
old biofilms. Neither agent affected viability of the biofilm over 96 h.
Biofilm growth rate, however, was decreased markedly over the first 8-10 h
of antibiotic treatment and was maintained at the reduced level for
approximately 40 h. Thereafter growth of the biofilms gradually returned to
pre-exposure levels. The pattern of recovery was different for the two
agents suggesting that different mechanisms might be involved. Accordingly
biofilms were exposed to successive and concurrent 24 h treatments with
vancomycin (5 mg/L) and teicoplanin (12 mg/L). This led not only to a
further 2-3 log reduction in the growth rate but also to a 3 log reduction
in the viability of the parent biofilm. Such synergy between the
glycopeptide agents might have therapeutic implications for the treatment
of E. faecalis infection.
ORIGINAL ARTICLES
In-vitro studies of the activity of glycopeptide combinations against Enterococcus faecalis biofilms
Department of Pharmacy, University of Manchester, UK.
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